1. Field of the Invention
The invention relates to an ink-jet recording ink set and ink-jet recording method, particularly to an ink-jet recording ink set suitable for forming a high quality image at a high speed using a plurality of liquids, and an ink-jet recording method.
2. Description of the Related Art
An ink-jet method for ejecting an ink from an ink ejection port such as a nozzle has been used for many printers since the printer is small size and inexpensive and non-contact printing of images on a printing medium is possible. Among these ink-jet methods, a piezoelectric ink-jet method by which ink is ejected by utilizing deformation of a piezoelectric element and a thermal ink-jet method by which ink droplets are ejected by utilizing boiling of the ink by thermal energy are featured in high resolution and high printing speed.
However, it has been a currently important problem to attain high printing speed and high image quality in printing on a plain paper sheet or a water impermeable recording medium such as a plastic sheet by application of the ink droplets using an ink-jet printer.
In ink-jet recording, ink (liquid) droplets are continuously ejected in the order of droplet a1, droplet a2, droplet a3 and so on up to droplet ax, and a line or an image is formed on the recording medium with droplet a1, droplet a2, and droplet a3 and so on up to droplet ax. It was practical problems that the image tends to be blurred and neighboring ink droplets a1 and a2 are mixed when permeation of the droplets after application takes a long period of time, and sharp images are prevented from being formed. Neighboring droplets after application are fused when the droplets are mixed to each other, and the movement of the droplet occurs. Consequently, the position of the droplet shifts from the applied position to cause irregular line width when thin lines are printed or to cause irregular color development when a colored image is printed.
One of the methods for suppressing the image blurring and irregular line width is to enhance hardening of the ink. A proposed technology thereof is to harden and fix the ink by radiation, not by evaporation of the ink solvent. Another proposed technology is to use a two-liquid ink for making the image fine and precise, wherein both ink components are allowed to react on the recording medium. For example, Japanese Patent Application Laid-Open (JP-A) No. 63-60783 discloses a method comprising the steps of applying a liquid containing a basic polymer on the recording medium, and recording an image with an ink containing an anionic dye. JP-A No. 8-174997 discloses a method comprising the steps of applying a liquid composition containing a cationic substance on the recording medium, and applying an ink containing an anionic compound and a colorant. Japanese Patent Publication No. 3,478,495 discloses a method using a liquid containing a photocurable resin and another liquid containing a photopolymerization initiator.
However, while these methods exhibit a certain effect for suppressing the image blurring, they are insufficient for solving the problems of irregular line width and uneven color tone caused by mixing between the droplets. Since the ink used in these methods contains an aqueous solvent, drying speed of the ink is slow, and decrease of the image quality is apprehensive due to a tendency of uneven distribution of precipitated dyes.
JP-A No. 8-218018 discloses a technology related to the above-mentioned technologies, wherein a pigment is used as a colorant and the ink is hardened and fixed with radiation. In this method, a pixel is formed by using any one of an ink containing a solidifying monomer and an ink containing a pigment dispersion followed by forming a pixel at the same point as the previously formed image using the other ink, and the ink is fixed using a UV light or an electron beam.
JP-A 2001-348519 discloses a technology using an ink composition including water, a reaction monomer and a colorant, and a coagulating solution containing a coagulating agent for allowing the ink composition to form precipitates, and the ink composition is applied after applying the coagulating solution on the recording medium. Japanese Patent Publication No. 3,642,152 discloses a technology in which an ink composition containing a monomer is applied after applying a reaction solution containing a photopolymerization initiator on the entire surface of the recording medium followed by irradiation of a UV light.
In addition to the above-mentioned technologies, JP-A No. 2000-135781 discloses a technology in which two different inks are applied so as to overlap to each other.